Here is an academic paper that gives some background introduction of the algorithm and hardware of RF focusing. I only took a brief look but FIGs. 40-41 appear to be an experimental demonstration of focusing in depth (around 1 meter).
https://www.researchgate.net/publication/347177646_Dynamic_Focusing_of_Large_Arrays_for_Wireless_Power_Transfer_and_Beyond
I have taken a good look at the paper of Hajimiri
et al. as referenced by nanotube in his post. BTW, this paper has been
published in the July issue of the IEEE JSSC, so it is very fresh!
It is a great read, providing all the serious engineering that we expect from a team out of Caltech. The paper focuses on the practical implementation of the necessary dynamic microwave beamforming and is extremely interesting since it seems they have done what WIGL should have in terms of theoretical analysis and HW prototyping.
Notably, they calculate the theoretical upper bound (stressing "theoretical", everything is optimal and simplifying assumptions are made) for the wireless power transfer (WPT) efficiency as a function of parameters such as the sizes of the antenna arrays, carrier wavelength and the transmission distance (and yes, let's not WIGL, the result is
in the best case inversely proportional to the square of the distance, this is actually not a debate). If we focus on ca 2.45GHz carrier frequency (which corresponds to the WIGL "demo" case), a theoretical upper bound of 10% at 1m is calculated for reasonable antenna arrays sizes (10cm x 10cm for the RX). With similar conditions, a >80% theoretical efficiency should be reached for a 10GHz frequency (which corresponds to the Caltech/Guru HW setup used for the paper).
As a conclusion, it seems that they indeed demonstrated that the transmission of a >2W DC power at ca 1m of distance seems to be feasible with some clever adaptive beamforming.
This being said, one specific thing bothers me a lot in this paper; I have not seen anywhere (unless I missed it) any mention of the power transmission efficiency, nor alternatively, any figure of the transmitted or consumed power by their so-called "generation unit" (GU) to obtain the figures shown. You'd think that they should have, given that they propose a way to calculate the theoretical upper bound for such an efficiency at the beginning of the paper. It would have been interesting to compare their results with the theory.
Anyway, I think that the discussion here would be more interesting based on the serious results proposed by the Caltech/Guru team rather than to continue blabbing about the marketing nonsense of the WIGL guys.
Any engineer from the Caltech/Guru team reading this? It would be very interesting (and fun) to continue the discussion and maybe see if you could challenge some of Dave's skeptical assertions on wireless power transfer.
As for me, I share the skepticism of many here, with the following key considerations:
- The main issue is always going to be the transmitted power. As already highlighted in several of the previous posts, even assuming a more-than-ideal situation where the wireless power transfer (WPT) would be 100% efficient, for applications where several Watts of available power would be required, we are always going to be outside any reasonable regulatory boundaries, especially considering the fact that the beamforming (by definition a non isotropic radiated power) needs to be factored in when calculating the EIRP compliance (or maybe some specific regulations could/should apply?)
- This is made even worse if you'd like/need to share the same power source between multiple consumers. You'd need to find a way to share it. In the Caltech/Guru paper, they propose a time multiplexing scheme, which in itself makes sense. However, you also have to consider that the average power available is also going to be divided by number of user (independently of the sharing scheme, no suprise here)!
- Even if regulatory requirements could be taken care of, thanks to heavy lobbying, you'd need to consider potential health hazards; do you really want to have your mobile phone charged by a focused microwave beam of >1W in your pocket right next to some interesting parts of your anatomy ?
- ... and I'm not even talking about cohabitation. Maybe easier if we don't target the crowded 2.4GHz ISM band, however, the rest of the spectrum is not free either! Not sure how this is proposed to be tackled... Maybe by getting specific spectrum allocated?
- Practical size(s) aspects; obviously, and this is clearly explained, the efficiency also depends directly on the sizes of the TX and RX antenna arrays. Depending on the targeted applications, this could obviously be a very limiting factor
- Environmental considerations; is it ethical to develop and promote a technology that, even if optimized, will always be significantly less efficient (energy wise) compared to using wires? Since this errs on the fringe of this forum's terms (no political topics), let's put it aside and focus on technical stuff, but still...